THE EUROPEAN SEAS. 



215 



deed each change in Jhe hinge structure has its 

 attendant external change ; and lastly, hinge teeth 

 altogether disappear. The hinge structure as a * 

 generic guide altogether fails, and the shells take 

 the external forms of Isocordia, Venericardia, 

 Crassatella, and Venus, yet they are all true Cardia, 

 and as aberrant forms are linked continuously one 

 with another, and lead back to the Cardium edule, 

 as the primary form. 



Fishes abound in the Caspian. In no part of the 

 world, Newfoundland excepted, are fisheries so pro- 

 ductive, or do they give employment to so large a 

 number of persons as they do about the mouths of 

 the rivers which discharge into this sea. 



Those principally taken are the great Silurus, 

 the great and lesser Sturgeon {Accipenser huso and 

 pragmilus), together with that most abundant but 

 less-esteemed species the Accipenser stellatus. 



Pallas mentions a circumstance which may serve 

 to convey some idea of the vast numbers of fish 

 which ascend the Sallian. The weirs for stopping 

 the fish are established where the river is 160 yards 

 broad and twenty-five feet deep. At these places 

 as many as 15,000 Sturgeon are taken a day ; but' 

 if the fishery is suspended for twenty-four hours, 

 the fish so accumulate that they become packed, 

 and fill the whole bed of the river to the level of 

 its banks. 



Lastly, Seals are as abundant in the Caspian as 

 they are in the Black Sea ; there are several species, 



